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My car is back firing a lot. I have no idea why. We changed the o2 sensor finally, tried new tunes (stock, street and racing bama tunes), cleaned the iac valve and idk what else to do :bash:

Any ideas?


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Are you throwing any codes? If not, tighten up everything in your exhaust system. I had a camaro that would backfire occasionally. Turned out I had a hole in the muffler (exhaust leak).
 

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Exhaust leak, bad valve(s), leaking injector(s), bad TPS...
 
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Here is what the shop manual says about P0122, and P0155. P0155 has the same possible causes as P0135.

What they have in common is a low voltage condition, one a low Vref (reference voltage) from the PCM. The other a low Vpwr (system [battery] power) level. This could be a wiring problem, or just low battery output.

Check the battery terminals to make sure they are clean and solidly connected, also check the voltage at the battery posts (the posts, not the terminals). It should be 12.6 V with the battery fully charged and stabilized (5 to 10 minutes after shutting down the engine)--if it is not then the battery is not charging properly.

If the battery post voltage is OK then check the voltage between the battery terminals, it should be close to the battery voltage not more than 0.1 V less. If it is less than that check the connections.

Next check the voltage between the positive battery terminal and the engine block. It too should be within 0.1 V of the battery voltage--if not there is a bad ground connection between the battery negative (ground terminal) and the block.

Monitor the battery voltage while cranking the engine, it should not drop below 10.5 V--if it does the battery has a bad cell, you will need a new battery or the battery is not fully charged. You can find the complete charging system description and diagnostic tests by going to my website and making these menu selections:

 

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Passenger upstream O2 sensor.


"Backfire" can mean a couple things. Is it misfiring and running like hell?
P0155 is for O² sensor 21, driver's side upstream sensor...

 
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